// Closure of Underground Cavities, Repository Design

LARYSSA

Long-term safety of closure systems in shafts and ramps in comparison

The access to a repository in a deep geological formation constitutes, similar to conventional mining, a critical bottleneck for the operation of such facilities. Through the surface accesses, all personnel and material flows are moved, and the underground facility is supplied with all necessary resources. The direct connection between the biosphere and the mine voids represents a potential ingress or egress pathway for fluids after the completion of the operational phase. Thus, its closure plays a crucial role within the multi-barrier system of a repository. The permanent closure aims to establish a condition that corresponds as closely as possible to the natural isolation potential of the geological barrier or the overlying protective layers. Despite this significant importance, operational, operational safety, and economic criteria are usually considered in the selection and design of surface accesses.

This project aims to investigate the long-term safety-relevant aspects of surface access closures and to compare the two basic concepts of a shaft or a ramp to identify and evaluate the differences relevant for demonstrating long-term safety. Shaft closure concepts are known for repositories in various host rocks; whereas closure systems specifically for ramps still need to be developed. The basis for this is provided by generic site models known from R&D projects, which have so far included shaft closures. Furthermore, the structural feasibility of ramp closures needs to be assessed, and a method for comparing closure systems and their sealing capability needs to be developed. The method will be applied to compare shafts and ramps within a repository system or host rock. The analysis aims to provide a comparison of the systems and will create an additional basis for decision-making regarding the choice of surface accesses.